Opportunists and Competitors
Growth, reproduction, and daily metabolism all require an organism to expend energy. The expenditure of energy is essentially a process of budgeting, just as finances are budgeted. If all of one’s money is spent on clothes, there may be none left to buy food or go to the movies. Similarly, a plant or animal cannot squander all its energy on growing a big body if none would be left over for reproduction, for this is the surest way to extinction.
All organisms, therefore, allocate energy to growth, reproduction, maintenance, and storage. No choice is involved; this allocation comes as part of the genetic package from the parents. Maintenance for a given body design of an organism is relatively constant. Storage is important, but ultimately that energy will be used for maintenance, reproduction, or growth. Therefore the principal differences in energy allocation are likely to be between growth and reproduction.
Almost all of an organism’s energy can be diverted to reproduction, with very little allocated to building the body. Organisms at this extreme are “opportunists.” At the other extreme are “competitors,” almost all of whose resources are invested in building a huge body, with a bare minimum allocated to reproduction.
Dandelions are good examples of opportunists. Their seed heads raised just high enough above the ground to catch the wind, the plants are no bigger than they need be, their stems are hollow, and all the rigidity comes from their water content. Thus, a minimum investment has been made in the body that becomes a platform for seed dispersal. These very short-lived plants reproduce prolifically; that is to say they provide a constant rain of seed in the neighborhood of parent plants. A new plant will spring up wherever a seed falls on a suitable soil surface, but because they do not build big bodies, they cannot compete with other plants for space, water, or sunlight. These plants are termed opportunists because they rely on their seeds’ falling into settings where competing plants have been removed by natural processes, such as along an eroding riverbank, on landslips, or where a tree falls and creates a gap in the forest canopy.
Opportunists must constantly invade new areas to compensate for being displaced by more competitive species. Human landscapes of lawns, fields, or flowerbeds provide settings with bare soil and a lack of competitors that are perfect habitats for colonization by opportunists. Hence, many of the strongly opportunistic plants are the common weeds of fields and gardens.
Because each individual is short-lived, the population of an opportunist species is likely to be adversely affected by drought, bad winters, or floods. If their population is tracked through time, it will be seen to be particularly unstable—soaring and plummeting in irregular cycles.
The opposite of an opportunist is a competitor. These organisms tend to have big bodies, are long-lived, and spend relatively little effort each year on reproduction. An oak tree is a good example of a competitor. A massive oak claims its ground for 200 years or more, outcompeting all other would-be canopy trees by casting a dense shade and drawing up any free water in the soil. The leaves of an oak tree taste foul because they are rich in tannins, a chemical that renders them distasteful or indigestible to many organisms. The tannins are part of the defense mechanism that is essential to longevity. Although oaks produce thousands of acorns, the investment in a crop of acorns is small compared with the energy spent on building leaves, trunk, and roots. Once an oak tree becomes established, it is likely to survive minor cycles of drought and even fire. A population of oaks is likely to be relatively stable through time, and its survival is likely to depend more on its ability to withstand the pressures of competition or predation than on its ability to take advantage of chance events. It should be noted, however, that the pure opportunist or pure competitor is rare in nature, as most species fall between the extremes of a continuum, exhibiting a blend of some opportunistic and some competitive characteristics.
Paragraph 1: Growth, reproduction, and daily metabolism all require an organism to expend energy. The expenditure of energy is essentially a process of budgeting, just as finances are budgeted. If all of one’s money is spent on clothes, there may be none left to buy food or go to the movies. Similarly, a plant or animal cannot squander all its energy on growing a big body if none would be left over for reproduction, for this is the surest way to extinction.
1. The word “squander” in the passage is closest in meaning to
○ extend
○transform
○ activate
○ waste
2. The word “none” in the passage refers to
○ food
○ plant or animal
○ energy
○ big body
3. In paragraph 1, the author explains the concept of energy expenditure by
○ Identifying types of organisms that became extinct
○ Comparing the scientific concept to a familiar human experience
○ Arguing that most organisms conserve rather than expend energy
○ Describing the processes of growth, reproduction, and metabolism
Paragraph 3: Almost all of an organism’s energy can be diverted to reproduction, with very little allocated to building the body. Organisms at this extreme are “opportunists.” At the other extreme are “competitors,” almost all of whose resources are invested in building a huge body, with a bare minimum allocated to reproduction.
4. According to the passage, the classification of organisms as “opportunists” or “competitors” is determined by
○ How the genetic information of an organism is stored and maintained
○ The way in which the organism invests its energy resources
○ Whether the climate in which the organism lives is mild or extreme
○ The variety of natural resources the organism consumes in its environment
Dandelions are good examples of opportunists. Their seed heads raised just high enough above the ground to catch the wind, the plants are no bigger than they need be, their stems are hollow, and all the rigidity comes from their water content. Thus, a minimum investment has been made in the body that becomes a platform for seed dispersal. These very short-lived plants reproduce prolifically; that is to say they provide a constant rain of seed in the neighborhood of parent plants. A new plant will spring up wherever a seed falls on a suitable soil surface, but because they do not build big bodies, they cannot compete with other plants for space, water, or sunlight. These plants are termed opportunists because they rely on their seeds’ falling into settings where competing plants have been removed by natural processes, such as along an eroding riverbank, on landslips, or where a tree falls and creates a gap in the forest canopy.
5. The word “dispersal” in the passage is closest in meaning to
○development
○growth
○distribution
○protection
6. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
○B(yǎng)ecause their seeds grow in places where competing plants are no longer present, dandelions are classified as opportunists.
○Dandelions are called opportunists because they contribute to the natural processes of erosion and the creation of gaps in the forest canopy.
○The term opportunists apply to plants whose seeds fall in places where they can compete with the seeds of other plants.
○The term opportunists apply to plants whose falling seeds are removed by natural processes.
Paragraph 7: The opposite of an opportunist is a competitor. These organisms tend to have big bodies, are long-lived, and spend relatively little effort each year on reproduction. An oak tree is a good example of a competitor. A massive oak claims its ground for 200 years or more, outcompeting all other would-be canopy trees by casting a dense shade and drawing up any free water in the soil. The leaves of an oak tree taste foul because they are rich in tannins, a chemical that renders them distasteful or indigestible to many organisms. The tannins are part of the defense mechanism that is essential to longevity. Although oaks produce thousands of acorns, the investment in a crop of acorns is small compared with the energy spent on building leaves, trunk, and roots. Once an oak tree becomes established, it is likely to survive minor cycles of drought and even fire. A population of oaks is likely to be relatively stable through time, and its survival is likely to depend more on its ability to withstand the pressures of competition or predation than on its ability to take advantage of chance events. It should be noted, however, that the pure opportunist or pure competitor is rare in nature, as most species fall between the extremes of a continuum, exhibiting a blend of some opportunistic and some competitive characteristics.
7. The word “massive” in the passage is closest in meaning to
○ huge
○ ancient
○ common
○ successful
8. All of the following are mentioned in paragraph 7 as contributing to the longevity of an oak tree EXCEPT
○ The capacity to create shade
○ Leaves containing tannin
○ The ability to withstand mild droughts and fire
○ The large number of acorns the tree produces
9. According to the passage, oak trees are considered competitors because
○ they grow in areas free of opportunists
○ they spend more energy on their leaves, trunks and roots than on their acorns
○ their population tends to increase or decrease in irregular cycles
○ unlike other organisms, they do not need much water or sunlight
10. In paragraph 7, the author suggests that most species of organisms
○ are primarily opportunists
○ are primarily competitors
○ begin as opportunists and evolve into competitors
○ have some characteristics of opportunists and some of competitors
Paragraph 5: Opportunists must constantly invade new areas to compensate for being displaced by more competitive species. Human landscapes of lawns, fields, or flowerbeds provide settings with bare soil and a lack of competitors that are perfect habitats for colonization by opportunists. █Hence, many of the strongly opportunistic plants are the common weeds of fields and gardens. █
Paragraph 6: Because each individual is short-lived, the population of an opportunist species is likely to be adversely affected by drought, bad winters, or floods. █If their population is tracked through time, it will be seen to be particularly unstable—soaring and plummeting in irregular cycles. █
11. Look at the four squares [█] that indicate where the following sentence could be added to the passage.
Such episodic events will cause a population of dandelions, for example, to vary widely.
Where would the sentence best fit?
12. Directions: Complete the table by matching the phrases below
Directions: Select the appropriate phrases from the answer choices and match them to the type of organism to which they relate. TWO of the answer choices will NOT be used. This question is worth 4 points.
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Opportunists
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Competitors
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●
●
●
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●
●
●
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Answer Choices
○Vary frequently the amount of energy they spend in body maintenance
○ Have mechanisms for protecting themselves from predation
○Succeed in locations where other organisms have been removed
○Have relatively short life spans
○Invest energy in the growth of large, strong structures
○Have populations that are unstable in response to climate conditions
○Can rarely find suitable soil for reproduction
○Produce individuals that can withstand changes in the environmental conditions
○Reproduce in large numbers
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參考答案：
1. ○4
2. ○3
3. ○2
4. ○2
5. ○3
6. ○1
7. ○1
8. ○4
9. ○2
10.○4
11.○3
12.○Opportunists：3, 4, 6, 9
○Competitors：2, 5, 8
機(jī)會主義者和競爭者
所有生物體都需要通過消耗能量來實(shí)現(xiàn)生長、繁殖和每日的新陳代謝。能量的消耗從根本上來說，是一個(gè)主體進(jìn)行能量預(yù)算的過程，如同財(cái)政預(yù)算。如果一個(gè)人所有的錢都用來買衣服，可能就沒錢購買食物或者看電影了。同樣，動植物不能將所有的能量都浪費(fèi)在生長巨大的軀體上，如果它們沒有多余的能量用于繁殖，那么必將走向滅絕。
因此，所有生物體都會將自己的能量進(jìn)行分配用以生長、繁殖、維系生命和進(jìn)行儲備。它們沒有選擇，這種分配方式是來自上一代遺傳基因的一部分。維系生命對于一個(gè)特定生物的身體設(shè)計(jì)是相對恒定的。儲備很重要，但儲備的能量最終都將被用于維系生命、繁殖或者生長。因此，能量分配上的主要不同就在于生長和繁殖之間。
一個(gè)生物體所有的能量幾乎都可以轉(zhuǎn)用于繁殖，基本沒有多少能量被分配用于生長。處于這個(gè)極端的生物體被稱作“機(jī)會主義者”。處于另一個(gè)極端的是“競爭者”，“競爭者”幾乎將其所有的能量都用于生長一個(gè)龐大的身軀，而僅用最低限度的能量進(jìn)行繁殖。
蒲公英是“機(jī)會主義者”典型例子。蒲公英的種子的頭部剛好生長到高出地面接觸到風(fēng)的高度，它們的體型也剛好是它們需要的最低尺寸，莖部是中空的，他們通過體內(nèi)水分來維持自身的硬度。蒲公英對身體最低限度能量的分配，使得他們成為一個(gè)散布種子的平臺。這些壽命短暫的植物大量繁殖；這就是說，他們在母體的周圍下一場種子雨。一旦種子落在了適合生長的土壤表面，新的生命體便會會迅速生長，但是，因?yàn)樗麄冮L成的軀體并不大，因此無法與其他植物競爭空間、水或陽光。這些植物被稱為機(jī)會主義者，因?yàn)樗麄円揽科浞N子落入那些競爭者們已經(jīng)被大自然淘汰了的地方生長而成活，如被侵蝕了的河岸、山崩之處或在由于樹木倒下而在森林冠層中形成的孔隙處等。
機(jī)會主義者必須不斷侵入新的領(lǐng)域，以抵消更具競爭力的物種對他們的擠兌。人工草坪、田地或花圃提供的光禿禿的土地，以及沒有競爭者的環(huán)境是“機(jī)會主義者”完美的棲息地。因此，人們田地和花園中常見的雜草多是擅長生長繁殖的機(jī)會主義植物。
因?yàn)槊總�(gè)個(gè)體的壽命短暫，機(jī)會主義植物的數(shù)量很可能受到干旱、惡劣的冬天天氣或者洪水等不利因素的影響。跟蹤它們一段時(shí)間，就會發(fā)現(xiàn)它們的數(shù)量特別不穩(wěn)定，在不規(guī)則周期內(nèi)飆升和暴跌。
與機(jī)會主義者相對應(yīng)的是競爭者。這些生物體往往有擁有龐大的身軀、壽命較長并且每年用在繁殖上面的能量相對較少。橡樹是典型的“競爭者”，一顆巨大的橡樹占據(jù)它的領(lǐng)地長達(dá)200年甚至更久，通過制造濃密的樹蔭和吸收土壤中任何多余水分驅(qū)逐所有可能的冠層樹木。橡樹的樹葉很難聞，其中富含丹寧酸，它會讓很多生物體感到不適或無法消化的化學(xué)物質(zhì)。丹寧酸是橡樹長壽的防衛(wèi)機(jī)制的一部分。雖然橡樹可以產(chǎn)生數(shù)以千計(jì)的橡子，但是，它們對大量的橡子投入的能量，和用于樹葉、樹干和根部生長的能量相比，簡直是微乎其微。一旦橡樹長成，在短周期的干旱甚至火災(zāi)中它都能夠輕易存活。橡樹的數(shù)量在一段時(shí)期內(nèi)似乎是相對穩(wěn)定的，它的存活可能更多地取決于它善于面對競爭或掠食的壓力，并非依賴于利用偶然事件。然而，值得關(guān)注的是，單純機(jī)會主義者或競爭者在自然界中是很少見的，大多數(shù)的物種都屬于這兩個(gè)極端組成的區(qū)域中，顯現(xiàn)出兼有二者的一些特征。
